1. Field of the Invention
The present invention relates to a device for measuring various quantities concerning a flow, especially, but not exclusively flow rate and flow velocity, among others, and relates to a flow rate and flow velocity measurement device sensitive to temperature and using a detection element integrally formed on a support body and/or a semiconductor chip, and also relates to a measurement device suitably applied, for example, as a combustion controlling mass flow rate sensor of an engine for a vehicle or industry, or a mass flow rate sensor for an industrial air conditioning system and compressor pressurized air supply system and, furthermore, an air/fuel ratio controlling sensor for a domestic gas hotplate.
2. Description of the Related Art
Recently, in situations concerning an automobile (especially, four-wheeled), attention to the environment by emission regulation and the like is deemed to be highly important. In order to cope with this regulation and the like, an engine combustion control of a higher accuracy has become necessary. Therefore, various proposals have been made in regard to a flow passage structure of an engine combustion controlling mass flow rate sensor. For example, in Japanese Patent Laid-Open No. 271293/1996 Gazette, Japanese Patent Laid-Open No. 120121/1983 Gazette, Japanese Patent Laid-Open No. 329472/1997 Gazette and Japanese Patent Laid-Open No. 287991/1997 Gazette, there is proposed a measurement device intended to realize a high accuracy flow rate measurement by means of making it difficult less susceptible to an influence caused by pulsation of the engine by a structure in which a divided flow pipe is connected to an intake pipe of the engine to take in the measurement fluid and a flow rate measurement is performed in the divided flow pipe.
However, according to the structure of the measurement device proposed in each of the above gazettes, since a flow passage structure of the divided flow pipe is not formed symmetrically with a detection element being made a center, in situations where a reverse flow (flow from the engine toward the outside air) through the intake pipe occurs, it is considered difficult to accurately measure the flow rate.
Therefore, an object of the invention is to provide a flow rate and flow velocity measurement device capable of, in regard to both of a normal flow and a reverse flow, performing measurements of a flow rate and a flow velocity stably and with a high accuracy.
Taking also, for example, a two-wheel vehicle into account, the present inventors have presumed that, not only in the case where the engine pulsates and so the flow in an intake pipe pulsates but also in the case where a fluid in the intake pipe flows in a reverse direction, in future it will become necessary to accurately measure its flow rate in order to realize a more accurate flow rate measurement. Therefore, the inventors provide a flow rate and flow velocity measurement device described below.
According to a 1st aspect, the invention provides a measurement device having: a divided flow pipe which has a divided flow pipe passage basically curved in U-shape form, and into which a flow in a main flow pipe, that is a detection object, is introduced; and a detection element which is disposed so as to be exposed to the flow in the divided flow pipe, and detects a quantity concerning the flow; wherein the divided flow pipe has a flow passage structure symmetrical with the detection element being made a center such that both of a normal flow flowing in a predetermined direction in the main flow pipe and a reverse flow flowing in a direction reverse to the normal flow can be equivalently (preferably, in the same level) detected.
In this manner, by forming the divided flow pipe so as to have the flow passage structure symmetrical with the detection element being made a center, i.e., by forming a divided flow passage shape into a structure symmetrical to a main flow direction in the main flow pipe with the detection element being made a center, since it is possible to accurately measure a flow rate and the like of both of the normal flow and the reverse flow and, further, since a sensor output equivalent to the normal flow is obtained in regard also to the reverse flow, this sensor output may not be compensated depending on whether a flow of the main flow M is the normal flow or the reverse flow. Accordingly, a control circuit and the like for compensating the sensor output in compliance with the flow direction become unnecessary, so that a miniaturization and an electric power saving of a sensor assembly are made possible.
Further, according to a 2nd aspect based on the aforesaid 1st aspect, the invention provides a flow rate and flow velocity measurement device having flow control means which is provided in the divided flow pipe, and forms such a flow as obliquely impinges against a detection face of the detection element.
According to such a flow control means, a flow to be detected is constantly supplied to the detection face of the detection element, so that it is considered that it follows that the flow to be detected surely flows on the detection face. In addition, in the vicinity of the detection face, since a generation of a turbulence, e.g., generations of a vortex flow and an exfoliation, is suppressed, it is considered that a detection accuracy and a reproducibility are improved.
According to a 3rd aspect, the invention provides a flow rate and flow velocity measurement device having: a divided flow pipe into which a flow in a main flow pipe, that is a detection object, is introduced; an inlet plate which basically extends in a direction basically orthogonal to a flow direction in the main flow pipe, and forms a divided flow pipe passage basically curved in U-shape form in the divided flow pipe; and a detection element which is disposed so as to be exposed to the flow in the divided flow pipe, and detects a quantity concerning the flow; wherein: one end of the inlet plate protrudes into the main flow pipe while passing through a top opening of the divided flow pipe such that the flow (irrespective of a normal flow and a reverse flow) in the main flow pipe is taken into the divided flow pipe passage; and the divided flow pipe has a flow passage structure symmetrical with the detection element being made a center.
According to this measurement device, by protruding the inlet plate into a main flow pipe passage, since it is possible to generate a measurement flow toward the detection element, the measurement device, among others a structure of the divided flow pipe, is greatly simplified or miniaturized. Especially, this measurement device is suitable as a measurement device concerning a flow in case where the main flow pipe is small in its diameter and/or in case where it is necessary to suppress a pressure loss to minimum. Further, in this measurement device, since the flow passage structure in the divided flow pipe is simplified, it is considered that an analysis of the flow is easy.
Other aspects and characteristics of the invention are set forth in each claim and, with its citation, a repetitionary description is omitted. Therefore, it is deemed that each characteristic of each claim is set forth here. Incidentally, a dependent claim can be applied respectively to each independent claim so long as it is not contrary to a principle of the invention set forth in each independent claim and, further, the dependent claim can be applied to another dependent claim.
Hereunder, preferred implementation modes of the invention are explained. In the preferred implementation mode of the invention, in order to realize a stabilized high accuracy measurement, a bypass flow passage short-circuiting between an inlet port and an outlet port of the divided flow pipe is added and/or a Venturi for throttling the divided flow pipe passage in the vicinity of the detection element is annexed. By the above bypass flow passage, a measurement fluid supply to the detection element is stabilized and, further, the measurement fluid (flow in the main flow pipe) becomes easy to be taken into the divided flow pipe. Further, by the above Venturi, on the detection face of the detection element, it is possible to effectively remove the turbulence of the measurement fluid. Thus, by these bypass flow passage and Venturi, in regard to both of the normal flow and the reverse flow, a measurement is stabilized and, further, a high accuracy measurement becomes possible.
Especially, in case where the flow passage structure of the divided flow pipe is formed symmetrically with the detection element being made a center like the invention, by providing an orifice reducing the above bypass flow passage or a flow sectional diameter of the bypass flow passage, it is possible to intend to further stabilize the flow reaching the detection element in regard to both of the normal flow and the reverse flow.
In the preferred implementation mode of the invention, the orifice is provided in the above bypass flow passage, and a flow rate of the measurement fluid toward the detection element is set by a protrusion amount of a flow passage wall forming the orifice or an orifice open area. By this, it is possible to quantitatively control the flow rate toward the detection element.
In the preferred implementation mode of the invention, in the divided flow pipe, there is provided means for forming such a flow as obliquely impinges against a detection face of the detection element. By this flow control means, the flow to be detected is constantly supplied to the detection face of the detection element, so that it is considered that it follows that the flow to be detected surely flows on the detection face. In addition, since generations of vortex flow and exfoliation in the vicinity of the detection face are suppressed, it is considered that a detection accuracy and a reproducibility are improved.
In the preferred implementation mode of the invention, as the flow control means for forming a down flow, i.e., a flow obliquely impinging against the detection face of the detection element or a flow flowing obliquely with respect to the detection face, there is provided a flow passage face (protuberance) protruding than the detection face in at least an upstream or an upstream and/or a downstream of the detection element. As a form of the above protrusion, one capable of forming the flow obliquely impinging against the detection face suffices and, preferably, it is protruded concavely or convexly or its protruding surface is made a linear, polygonal or concave curved form slant face.
In the preferred implementation mode of the invention, in a curved portion of the divided flow pipe (detection pipe), the detection face of the detection element is exposed inside the divided flow pipe. Further preferably, a curved pipe (divided flow pipe) is attached in a direction orthogonal to the main flow pipe (measurement object pipe), and the detection element is provided in this curved portion (folded portion, a portion where the flow passage is curved) of the divided flow pipe. Alternatively, the detection element is disposed in a portion where the flow in the divided flow pipe is inverted or a portion where the flow direction is sharply changed or its vicinity. Also preferably, the detection face of the detection element is exposed to a portion where the flow in the divided flow pipe is speedy. Also preferably, the detection face of the detection element is exposed to a portion where the flow is throttled and subsequently changed in its direction in the divided flow pipe or its vicinity.
In the preferred implementation mode of the invention, the detection element attached to a bottom wall of the divided flow pipe is positioned outside the main flow pipe. By this, an attachment and an exchange of the detection element become easy, and also it becomes easy to take out an output of the detection element.
In the preferred implementation mode of the invention, such a detection element as mentioned below is used. That is, this detection element is one in which basically four thin film resistors are provided in a semiconductor chip. More concretely, a diaphragm portion and a rim portion are provided on a semiconductor layer. In the diaphragm portion, there are provided (1) an upstream temperature sensor, (2) a downstream temperature sensor, and (3) a heater disposed between the upstream temperature sensor. On the other hand, in the rim portion, there is provided (4) an atmosphere temperature sensor. The diaphragm portion is made very thin and a heat insulation is intended.
Next, a principle of detecting various quantities concerning a flow such as flow velocity and flow rate by using this detection element is shown.
(1) An electric power supplied to the heater is controlled such that the heater has a constant temperature difference with respect to an atmosphere temperature.
(2) Accordingly, in case where there is no flow, temperatures of the upstream temperature sensor and the downstream temperature sensor are approximately the same.
(3) However, in case where there is the flow, the temperature of the upstream temperature sensor descends because a heat escapes from its surface. As to the temperature of the downstream temperature sensor, since a heat input from heater increases, a temperature change is smaller than that of the upstream temperature sensor. Incidentally, there is also a case where the temperature of the downstream temperature sensor ascends.
(4) On the basis of a temperature difference between the upstream temperature sensor and the downstream temperature sensor, the flow rate and the flow velocity etc. are detected and, from a sign of the temperature difference, a flow direction is detected. Incidentally, the above temperature difference can be detected on the basis of a change in electrical resistance by the temperature.
In the preferred implementation mode of the invention, it is one for, on the basis of temperature, measuring the quantity concerning a flow, at least including a flow rate and/or a flow velocity by the detection element.
In the preferred implementation mode of the invention, the measurement device according to the invention is installed in an intake system of engine of various vehicles, and can be applied to a measurement of intake quantity etc. of the engine mounted on a two-wheel or four-wheel vehicle. For example, the measurement device according to the invention can be installed between an air cleaner and a throttle valve in the intake system of engine mounted on the four-wheel vehicle. Further, the measurement device according to the invention can be attached, in the intake system of an engine mounted on the two-wheel vehicle, to a two-wheel vehicle intake pipe (air funnel) connected to a cylinder in order to measure a flow rate or a flow velocity etc. of the intake.